Telechelic polymers (i.e., polymers having terminal functional groups) can be used in a variety of applications, such as the manufacture of adhesives, sealants, coatings, films, fibers, and the like. These polymers have typically been prepared using dilithium initiators. See U.S. Pat. Nos. 5,393,843 and 5,405,911. For example, reaction of two equivalents of an alkyllithium reagent, such as sec-butyllithium, with a compound having at least two independently polymerized vinyl groups, such as isomeric divinylbenzenes or isomeric diisopropenylbenzenes, generates a dilithium initiator. Addition of an anionically polymerizable monomer, such as 1,3-butadiene, isoprene, or styrene, affords a polymer chain with living anions on each of the two termini (a "dianion"). This dianion can then be quenched with various functionalizing agents to afford a telechelic polymer.
These functionalization reactions, however, are often inefficient, due to the formation of physical gelation phenomena that produce severe mixing problems. See L. Weber, Makromol. Chem., Macromol. Symp., 3, 317 (1986) and U.S. Pat. Nos. 5,393,843 and 5,478,899. In addition, polymers prepared from dilithium initiators necessarily have the same functional group on each termini (are "homotelechelic").
Electrophiles that contain protected functional groups have been employed to functionalize polystyryl lithium and polyisoprenyl lithium. For example, Deffieux and co-workers reported that chloroacetals afforded high yields of functionalized polystyrene. See Polymer International 41, 453 (1996). Additional references to the use of protected functionalized electrophiles include: M. Tokyamo, A. Hirao, S. Nakahama and K. Takenaka, Macromol. Chem. Phys., 197, 3135 (1996); A. Hirao, H. Nagahama, T. Ishizone, and S. Nakahama, Macromolecules, 26, 2145 (1993), and K. Ueda, A. Hirao, and S. Nakahama, Macromolecules, 23, 939 (1990). The polymers produced in each of these syntheses, however, are monofunctional.